Process for making light-developable direct-writing silver halide emulsions containing rhodium or iridium

ABSTRACT

Process for preparing light-developable, direct-writing silver halide emulsions, e.g., emulsions for oscillograph recording elements which comprises digesting such an emulsion in the presence of a rhodium or iridium salt at pH below 6.0 and then adding a halogen acceptor.

United States Patent Inventor John Howard Bigelow Rochester, N.Y.

June 22, 1967 Oct. 26, 1971 E. I. du Pont de Nemours and Company Wilmington, Del.

Appl. No. Filed Patented Assignee PROCESS FOR MAKING LIGHT-DEVELOPABLE DIRECT-WRITING SILVER IIALIDE EMULSIONS CONTAINING Rl-IODIUM OR IRIDIUM [56] References Cited UNITED STATES PATENTS 2,717,833 9/1955 Wark 96/108 3,000,739 9/1961 Maffett..... 96/108 3,178,293 4/1965 Bige1ow.... 96/108 3,206,313 9/1965 Porter 96/108 3,287,137 11/1966 McBride... 96/108 3,418,122 12/1968 Colt 96/108 3,449,125 6/1969 Bigelow 96/108 2,448,060 8/1948 Smith c 96/108 3,447,927 6/1969 Bacon et a1 96/63 OTHER REFERENCES Glatkides, Photographic Chemistry p. 318

Primary Examiner-Norman G. Torchin Assistant Examiner-M. F. Kelley Attorney-Lynn Barratt Morris ABSTRACT: Process for preparing light-developable, directwriting silver halide emulsions, e.g., emulsions for oscillograph recording elements which comprises digesting such an emulsion in the presence of a rhodium or iridium salt at pH below 6.0 and then adding a halogen acceptor.

PROCESS FOR MAKING LIGHT-DEVELOPABLE DIRECT-WRITING SILVER I-IALIDE EMULSIONS CONTAINING RHODIUM OR IRIDIUM BACKGROUND OF THE INVENTION 1 Field of the Invention:

This invention relates to light-developable, direct-writing oscillographic recording elements having improved sensitometric characteristics. The present invention constitutes an improvement in the image access time of light-developable direct-writing oscillographic recording element by the step of digesting a silver halide emulsion, whose silver halide grains have been precipitated in the presence of plumbous ions, at a pH below 6.0 in the presence of rhodium or iridium salts. The step of digestion in the presence of rhodium or iridium salts appears to promote low-intensity reciprocity failure which is believed to be the mechanism by which light-developed, direct-writing images are obtained.

2. Description of the Prior Art Light-developable, direct-writing oscillographic recording papers are described in US. Patents Hunt US. Pat. No. 3,033,678 and No. 3,033,682 May 8, 1962, Bigelow No. 3,178,293 Apr. 13, 1965, Hunt No. 3,183,088 May 11, 1965, Hunt No. 3,189,456 June 15, 1965, and Hunt No. 3,249,440 May 3, 1966. None of these patents describe the addition of rhodium or iridium salts to light-developable, direct-print (or direct-writing) silver halide emulsion layers during the digestion stage of their preparation. In these patents there are described various such direct writing silver halide emulsion processes for the manufacture thereof, which layers are present in radiation sensitive elements for recording the highintensity light traces from oscillographic recording instruments. Such elements require no chemical processing and are developed by exposure to a source of radiation of lower intensity than the image forming high-intensity source. Emulsions for the direct writing elements of the above patents can be made by precipitating silver halides in a macromolecular organic colloid, e.g., gelatin, coagulating, washing the coagulated emulsion, redispersing, digesting and either during or after digestion adding a powerful halogen acceptor and a background stabilizer and coating. Preferably, the silver halide, e.g. silver chloride as in the case of US. Pat. No. 3,178,293, is precipitated in the presence of a plumbous ion and then sufficient soluble bromide is added to convert a substantial portion of the silver chloride to silver bromide. The emulsion is coagulated, washed and redispersed in the manner described in Moede U.S. Pat. No. 2,772,165 Nov. 27, 1956. A halogen acceptor, e.g., stannous salt, is added and the emulsion digested and after the addition of final adjuvants, e.g., hardeners, buffers, etc. the emulsion is coated.

A disadvantage of the previous direct-writing layers is that image access time is excessive. That is, the time interval between when the high-intensity light trace is recorded, and when the trace image becomes visible under exposure to lightdeveloping lower intensity radiation, is too long. It is a major objective of these direct-writing papers to make the image visible by light development in the least amount of time possible.

SUMMARY OF THE INVENTION This invention pertains to a process for making a lightdevelopable, direct-writing colloid-silver halide emulsion which comprises 1. precipitating silver chloride in an aqueous acidified solution of a water-permeable organic colloid binding agent in the presence of 0.0033 to 0.1 mole of a water-soluble plumbous salt per mole of silver;

2. ripening the precipitated emulsion at about 100 F.-l60 F. for about 5-50 minutes;

3. adjusting the pH to about 6.0, e.g., with dilute HCl;

4. mixing with 50 to 160 mole per cent of a water-soluble inorganic bromide,

5. mixing 8.45 10 to 4.22 l0 mole per cent of a rhodium salt (8.45X10 to 4.22X10' mole per mole of silver) or 4.58Xl0 to 8.9X10 mole percent of an iridum salt (4.58X10'" to 8.9X10 mole per mole of silver),

6. digesting the resulting emulsion for 5 to 30 minutes at 1 10 to 130 F. and prior to completion of digestion or to coating, incorporating therewith, based on the silver a. 0 to mole percent of a water-soluble inorganic bro-' mide,

b. 0 to 5 mole percent of a water-soluble plumbous or cupric salt,

c. a halogen acceptor.

The emulsion is then coated onto a suitable support.

The precipitation can be accomplished by using any of the water-soluble silver salts and water-soluble halides described in the patents listed above but is preferably carried out as claimed in Hunt US. Pat. No. 3,178,293 by admixing silver nitrate and plumbous salt in aqueous solution with an aqueous acidified solution of the colloid and water-soluble halide.

An important point is that the rhodium or iridium salt be added at the start of digestion and after the conversion of a substantial part of the silver chloride to silver bromide. Suitable rhodium and iridium salts include rhodium trichloride (hydrated), rhodium nitrate, ammonium chlororhodate; iridium tetrachloride. iridium tetraiodide and iridium chloroiridate. The process has the advantage that the resulting direct-writing, light-developable silver halide emulsions, have rapid image access time by light-development. Where iodine, alkali metal nitrites and other halogen acceptors except tine salts are used, emulsions of this invention may also be chemically processed in conventional alkaline photographic developer and fixing solutions.

Suitable other water-soluble silver salts and water-soluble halides for making the silver halides are listed in Maffet, US. Pat. No. 3,000,737, Sept. 19, 1961.

After the addition of soluble bromide (Step 4) the emulsion may or may not be, but preferably is washed in the manner described in Moede US. Pat. No. 2,772,165. The emulsion is redispersed and digested as described above. At this point or DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred halogen acceptors for this invention are potassium iodide and stannous chloride. In general from 0.5 to 120 mole percent and preferably 5 to 40 mole percent of a stannous salt based on the silver may be used or 0.2 to 2.0 mole percent of potassium iodide may be used. Rhodium chloride and potassium chloroiridate are preferred as the rhodium and iridium salts. After the digestion step, the usual coating adjuvants, e.g., hardeners, wetting agents, etc. are added and the viscosity is adjusted as desired by the addition of a further quantity of gelatin or other colloid. In general, the ratio of gelatin to silver halide is 2:1, however, this not at all critical. The prepared emulsion is then coated on a suitable support, e.g., paper and dried to give a dry coating weight equivalent to about 30 mg. AgBr/dm..

To determine the sensitometric characteristics of the material it may be exposed through a power of 2 step wedge in an electronic flash tube sensitometer similar to that described by Wyckoff and Edgerton, Journal of the Society of Motion Picture and Television Engineers, 66, 474 (1957). This instrument has a xenon discharge tube as the source of radiation and has available two exposure times of 10 and 1.000 microseconds. The exposed material may be light developed by irradiation under cool whitefluorescent lighting at about 95 foot-candle intensity. To determine the densities of the image and background, a reflection densitorneter may be used whose values correspond to visual density. To test image access time, the material was exposed at 0.001 second on an Samples are exposed on Edgerton, Germeshausen and Grier Mark Vl sensitometer at 0.00l

sec. and light developed under daylight fluorescent light at 95 Edgerton, Germeshausen and Grier Mark V] sensitometer and 5 light-developed by irradiation under the cool white -n. candles. Ah arbitrary rating ofaccess time is applied in which I fluorescent lighting described above. An arbitrary numerical is fastest 2 designation of time necessary for image to appear is given with number 1 being the fastest Expose on Edgerton Germeshausen and Grier Mark VI sensitometer at 0.00]

The following examples further illustrate but are not inscchlhmughapowderofz tended to limit the scope of the invention.

' step wedge. Light develop by irradiation from daylight fluorescent lamps at an in- EXAMPLE I tensity level ofSO 41. dl B k d=4 An initial gelatmo-sllver chloride emulsion was made by can as M 8mm slowly adding an aqueoussolution containing a mixture of l Densities Md on reflection dcnsiwmewrmole of Sflver nltrfne 0033 f q of lead Background=density differencehetween white paperandlightdeveloped sample. Pb(NO to a gelatin solution contalnlng 1 mole of potassium chlorid d a idifi d ith 0 05 l f'h d hl i acid D-max=density difference between background and maximum step density. The precipitation was carried out under a Wratten Series 1 safelight manufactured by the Eastman Kodak Company. The temperature at precipitation and for 40 minutes thereafter was EXAMPLE n i a at A 9 f f z i i 5 Example I was repeated with rhodium chloride added to 2; 0 p0 F a ff z a e at h T egmmfig e seven portions of an emulsion but with the various ingredients minute P w 1 e e F e d at 160 he added after digestion in example I left out of the samples as inresultlng silver chlorobromlde emulsion was coagulated, dicated in washed, and redispersed similarly to the process described in i M de U S Pat No 2 772 5 Th 1 following table to show that rhodlum is the vltal lngredlent in reducing image acf e emu slon was cess time. A commercial oscillographic recording element was also tested. The redlspersed and gelatin necessary to provlde about 9 percent results are shown below.

TABLE II.-Rh+ THE IMPORTANT INGREDIENT IN FAST ACCESS Emulsion I Sensisample tlzlng Chrome Back- Access number NBzSOa dye KBr Pb(NOa)z alum Din" ground time Yes Yes Yes Yes Yes .20 .18 1 No Yes Yes Yes Yes 30 14 1 Yes Yes No Yes Yes .26 .24 1 No Yes No No No .24 .24 1 N 0 Yes Yes No Yes .32 16 1 No No Yes No No .34 18 1 N 0 Yes Yes No N o 30 l6 1 Yes No Yes Yes 3 Yes concentration for coating and HCl to give a pll=4.5 was added. The emulsion was divided into six equal parts and the different molar quantities of rhodium chloride per mole of silver as indicated in the table below were added to the emulsion, the sixth portion served as a control and contained no rhodium chloride. The emulsions were optically sensitized with the optical sensitizing dye, 3-ethyl-dihydrobenzoxalylidene-Z 5'-isopropylidene-3-ethyl-2-thio-4'-ketotetrahydrooxazole and then digested for 20 minutes at 130 F. AFter digestion, there were added to each emulsion 0.01 mole of potassium iodide, 0.6 mole of potassium bromide, 0.02 mole All samples except commercial sample contain 4.2)(10 mole Rh lmole' AG.

EXAMPLE lll TABLE III.-Rh+ PLUS VARIOUS SENSITIZING DYES of plumbous nitrate, coating aids and chrome alum as a gelatin Amount k sensitizing Bac hardener. The pH was ad usted to 3.5 10.1 and the emulsion dye/mole Aw Dmw ground Access was coated on paper to give a dry coating welght equivalent to 30 mg. of AgBr per square decimeter. The emulsion was dried R? 01 29 18 1 in a conventional manner. Tested on the flash tube sensitome- .g i ter as described above the light-developed image access time 4 1 was found to be reduced with those emulsion samples contain- Commercial sample None 2 ing rhodium chloride as indicated in the following table.

All samples except commercial sample contain 4. ZXlO" mole Riv /mole Ag.

*A 3,3 TABLE I '-diethyl-5.5

'-" 'hyl oxacarbocyanine iodide.

Method B 3 Emulsion Back- Access 51mm]e M015 RW/Mole s DMflX ground Time -ethyl-dihydrobnzoxalylidene-ZzS 2 4.22Xl0" 0.27 0.! l l -isopropylidene-3 3 1.69xl0" 0.26 on 1 4 8.45Xl0 0.27 012 l y 6 None 0.28 o. l l 2+ 7 5 '-keto-tetrahydro-oxazole.

EXAMPLE IV TABLE IV CONCENTRATION OF Ir AT REMELT Sample Back- Image No. Moles lr 'lmole Ag D-max ground Access 1 4.58 l" 0.24 0.14 l 20 2 2.26X10 0.25 0.13 l

3 83x10" 0.26 0.12 l 4 458x10" 0.30 0.12 l 5 226x" 0.29 0.10 l 6 8.9X10 0.32 0.10 l 7 None 0.22 0.15 2

EXAMPLE V Example IV was repeated except that the emulsion was not optically sensitized and the amount of potassium chloroiridate as shown in table V were added. Sample 6 did not contain any of the iridium compound and was used as a control. It would appear that 4.5 X10" moles of iridium compound per mole of silver is approaching the lower limit in effectiveness in reducing the image access time.

TABLE V.

Moles Ir Backmole Ag+ Dm ground Access Coating Number: 1 3. 3X10- .11 .05 1 2 26 10- .14 .18 1 4 58 10' 16 18 1 8. 9X10 18 14 1 4 58 10- 18 16 1+ None 22 22 2 Exposure was 0.0001 second on the sensitometer referred to in example 1.

EXAMPLE VI Example I was repeated through the steps of washing, redispersing and pH adjustment. There was then added 4.2X10 mole of rhodium chloride per mole of silver and the emulsion was digested for 25 minutes at 130 F. with 0.467 mole of potassium bromide, 0.02 mole of plumbous nitrate Pb(NO and 0.2 mole of stannous chloride (SnCl as the halogen acceptor, buffers, coating aids and sufficient dilute hydrochloric acid to adjust the pH to about 2.4. As indicated in the table an optical sensitizing dye (Dye B of example III) was added to samples land 3, No. 3 being a control which did not contain the rhodium compound. The results are shown in Table VI.

Expose on Edgerton, Germeshausen and Grier Mark Vl sensitometer at 0.0001

sec thru a power of 2 wedge. Light develop by irradiation from daylight fluorescent lamps at an intensity level of 50 ft. candles for 4 min. Read densities on reflection densitometer.

Bkgrd. density difference between white paper and light developed sample D-max= density difference between background and maximum step density Samples are exposed on Edgerton, Germeshausen and Grier Mark Vl sensitometer at 0.0001

sec. and light developed under daylight fluorescent light at ft. candles. An arbitrary rating ofaccess time is applied in which 1 is fastest.

Stannous chloride may be added from aqueous solution, particularly when such solutions are made using the anhydrous stannous compound. However, the stannous salt may also be added from ethanol, cellosolve, glycerine, dilute hydrochloric acid, etc.

Where it is desired, other halides or combinations of halides may be used to form the silver halide grains. For example, pure silver chlorobromide or silver chlorobromide may be used. When soluble chloride salts are used it is desirable, because of solubility differences, to form the silver halide grains of desired size and then add sufficient soluble bromide salts to provide the desired concentration of bromide ions.

Although the mechanism of the reaction of rhodium and iridium salts on the system is not completely understood, it is believed that rhodium (Rh or iridium Ur) occupy some otherwise photolyzable surface sites to increase the low intensity reciprocity failure, and to displace these sites into deeper crystal layers where a greater concentration of photolyzable sites allow more rapid access to the exposed image.

In place of the gelatin binding agent used in the foregoing examples there can be substituted other material or synthetic water-permeable organic colloid binding agents, including the binding agents listed in Hunt, U.S. Pat. No. 3,033,682.

Suitable supports for the novel photographic emulsions of this invention include those used in the prior art on oscillographic recording element. The preferred support is a photographic grade paper but may be a hydrophobic film composed of a cellulose ester, e.g., cellulose acetate or a polymer, e.g., polyester films disclosed in Alles et al., U.S. Pat. No. 2,627,088 and Alles U.S. Pat. No. 2,779,684.

The novel process of this invention produces lightdevelopable, direct-writing, photosensitive emulsion layers and elements having several advantages over the prior art materials. The emulsion layers and elements upon exposure to high-intensity radiation and subsequent light-development, yield images of high maximum density and good stability against image fading. In addition, the image access timeis greatly reduced as compared to the recording elements of the prior art. The elements are extremely convenient to use because wet processing can be eliminated. However, the elenients are adaptable to conventional chemical development and fixing when a halogen acceptor other than tin is used. The elements may be subjected to relatively high intensity illumination for long periods of time without a substantial change in the image characteristics. The elements can be used to reproduce photographically the image record by high-intensity exposing radiation and without serious image deterioration. The elements have high photographic speed and also may be processed in the manner disclosed in the Hunt and Bigelow patents referred to above including Hunt U.S. Pat. No. 3,033,682 and Bigelow U.S. Pat. No. 3,178,293.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for making a light-developable, direct-writing,

water-permeable organic colloide-silver halide emulsion which comprises:

2. ripening the precipitated emulsion at about 100 F.l60

F. for about -50 min.;

5. A process according to claim 1 wherein said plumbous salt is plumbous nitrate and said inorganic bromide is potassium bromide.

6. A process according to claim 1 wherein the pH is ad- 5 justed with dilute l-lCl.

7. A process for making a light-developable, direct-writing, water-permeable organic colloid-silver halide emulsion which comprises 1. admixing aqueous silver nitrate and 0.33- mole per- 3. adjusting the pH to about 6.0; 10 cent of a water-soluble plumbous salt with an acidified 4. admixing from 50 to 160 mole percent of a water-soluble aqueous solution of a water-soluble chloride containing a inorganic bromide; water-permeable organic colloid binding agent; 5. admixin x10 to 4,22x10 l percent f a water- 2. ripening the precipitated emulsion at about 100 F.l60

soluble rhodium salt or 4.58Xl0 to 8.9Xl0 mole per- -f f milk; cent of a water-soluble iridium salt, l l g the P" F about 6. digesting the resulting emulsion for 5 to 30 minutes at fldmlxlllg from to 160 mole W Ofa water'solubie l10l30F. and prior to completion of digestion or to f l bromlde; coating, incorporating therewith, based on the silver admlxmg 845x10"; to 422x10" mole p of a a. 0 to 120 mole percent of a water-soluble inorganic browatel'soluble rhodium Salt 453x10" to 89x10" H1016 mide, percent of a water-soluble iridium salt. 0 to 5 mole percent f a watebsoluble plumbous or 6. digesting the resulting emulsion for 5 to 30 minutes at cupric salt, ll0-l30F. and prior to completion of digestion or to a h l acceptor. coating, incorporating therewith, based on the silver 2 A process according to claim 1 wherein gelatin is the a. Oto 120 mole-percent of a water-soluble inorganic broganic colloid. mlde,

3. A process according to claim 1 wherein said rhodium salt 0 5 mole PMcent of a lam-Soluble plumbous is rhodium chloride. cuprlc Salt 4. A process according to claim 1 wherein said iridium salt a halogen acceptor' is potassium chloroiridate. 

2. ripening the precipitated emulsion at about 100* F.-160* F. for about 5-50 min.;
 2. A process according to claim 1 wherein gelatin is the organic colloid.
 2. ripening the precipitated emulsion at about 100* F.-160* F. for about 5-50 min.;
 3. adjusting the pH to about 6.0;
 3. A process according to claim 1 wherein said rhodium salt is rhodium chloride.
 3. adjusting the pH to about 6.0;
 4. admixing from 50 to 160 mole percent of a water-soluble inorganic bromide;
 4. A process according to claim 1 wherein said iridium salt is potassium chloroiridate.
 4. admixing from 50 to 160 mole percent of a water-soluble inorganic bromide;
 5. admixing 8.45 X 10 3 to 4.22 X 10 4 mole percent of a water-soluble rhodium salt or 4.58 X 10 2 to 8.9 X 10 4 mole percent of a water-soluble iridium salt.
 5. A process according to claim 1 wherein said plumbous salt is plumbous nitrate and said inorganic bromide is potassium bromide.
 5. admixing 8.45 X 10 3 to 4.22 X 10 4 mole percent of a water-soLuble rhodium salt or 4.58 X 10 2 to 8.9 X 10 4 mole percent of a water-soluble iridium salt,
 6. digesting the resulting emulsion for 5 to 30 minutes at 110-130* F. and prior to completion of digestion or to coating, incorporating therewith, based on the silver a. 0 to 120 mole percent of a water-soluble inorganic bromide, b. 0 to 5 mole percent of a water-soluble plumbous or cupric salt, c. a halogen acceptor.
 6. A process according to claim 1 wherein the pH is adjusted with dilute HCl.
 6. digesting the resulting emulsion for 5 to 30 minutes at 110-130* F. and prior to completion of digestion or to coating, incorporating therewith, based on the silver a. 0 to 120 mole percent of a water-soluble inorganic bromide, b. 0 to 5 mole percent of a water-soluble plumbous or cupric salt, c. a halogen acceptor.
 7. A process for making a light-developable, direct-writing, water-permeable organic colloid-silver halide emulsion which comprises 